This invention relates generally to a yarn winding apparatus and more particularly to an improvement in a winding apparatus with dual traverse devices.
In yarn winding devices for forming generally cylindrical packages with substantially flat ends of the type employing either a center drive or a surface drive for rotating the yarn package, it is customary to use a yarn traverse mechanism comprising a barrel type traverse cam with right-hand and left-hand helical portions joined by curved reversals for driving a combined traverse cam follower and yarn guide back and forth between parallel fixed guide rails. The cam reversal portions are usually kept as short as possible, consistent with traverse guide rate of acceleration and rate of change of acceleration in the interest of minimizing shoulder build-up or other malformations on the yarn package. In effect, this imposes an upper limit on the speed at which yarn may be wound since operation at speeds higher than the design speed would result in early destruction of the traverse cam follower.
One way of reducing the effect of high accelerations encountered in barrel cam traverses is to use a dual mode traverse as taught generally by Schippers et al., U.S. Pat. No. 3,797,767 and U.S. Pat. No. 3,86l,607 which employ in addition to a driven reciprocable thread guide, a second traversing device in the form of a grooved traverse roll to take over the thread traverse stroke near the respective ends of the traverse stroke of the reciprocable thread guide. A synchronous drive keeps the two traverse mechanisms in step with each other.
Schippers' apparatus has shortcomings in that the grooved traverse roll has a groove configuration such that an appreciable length of yarn (called "uncontrolled yarn length", UYL) extends from the last point of controlling contact on the traverse roll to the actual point of laydown on the package surface; this means that despite the fact that the groove reversal may be "sharp", meaning that it has a small radius, the actual pattern of yarn laydown in the package reversal has a comparatively larger radius accompanied by a loss of stroke and the depositing of more yarn at the respective ends of the package than in the intermediate portions. Further, in the Schippers' apparatus disclosed in U.S. Pat. No. 3,861,607, the package surface is spaced a significant distance away from the grooved roll, being driven from yet another roll. Thus, the uncontrolled yarn length is even longer.
In prior art winders of this type, measures aimed at producing a short yarn laydown curvature, where long uncontrolled yarn length exists, include increasing the groove stroke, sharpening the groove reversal radius and introducing "cutback" (an increase in groove helix angle) on the recess side of the reversal. While such measures may be partially effective in reducing the radius of curvature of the yarn laid on the package, the distorted groove path makes it more difficult for the reciprocating traverse guide to deposit yarn in the groove.
Further, in these prior art type winders, the grooved traverse roll is generally located beneath the first reciprocating traverse such that the yarn length from traverse guide to first point of contact on the grooved roll is quite large further aggravating the problem of having the reciprocating traverse deposit the yarn in the groove of the grooved roll. Again, the effect of this long uncontrolled yarn length between the traverse means is to reduce the stroke of the yarn at its point of entry to the grooved roll, and to modify and increase the radius of yarn laydown curvature generated by the reciprocating guide. The resulting mismatch between the milder reversal curve and shortened stroke of the yarn laid down on the grooved roll by the reciprocating guide and the sharp curve, increased stroke, and "cutback" of the groove will tend to cause the yarn to climb out of the groove. Means of counteracting this tendency include increasing the stroke, sharpening the curvature of the traverse cam track reversal, and adding "cutback" at approach and/or recess, all of which increase the forces on the reciprocating guide and therefore reduce its life at high speeds. Yet another attempted cure is to widen and deepen the roll groove to insure capture and retention of the yarn, which as before stated, increases the uncontrolled yarn length of roll to package and also may cause lateral scrubbing of the yarn when the yarn is dragged over the groove edge. Thus, this general design tends to be self-defeating.
Additionally, when grooves are made deeper in the reversal area relative to groove depth in other portions of the roll, yarn tension at the reversals may increase (where a tension increase is highly undesirable) owing to the changed frictional drag effect of the groove, the surface velocity of the root of the groove having been decreased in proportion to its reduced radius.